The present invention relates to an electromagnetic mold for continuous casting having side and endwalls each of which comprises an inductor part with inductor loop and a screen such that at least one endwall can be displaced along and secured to the sidewalls by means of releasable bolts, while the related inductor parts and screens are connected to closed loops via a clamping facility with pistons in piston chambers.
Using such electromagnetic molds for direct chill casting the molten metal is poured at a given rate onto a dummy block situated within a loop-shaped electrical inductor. High frequency alternating current in the inductor generates an electromagnetic field which constrains the molten metal horizontally within the inductor in a shape which is essentially determined by the inner contours of the inductor loop. By jetting with coolant, for example water, the metal at and close to the surface solidifies rapidly as the strand is lowered.
Such equipment usually features an electromagnetic screen which is tapered downwards. This is mounted coaxially within the inductor and is made of metal (for example stainless steel). The shape of this screen has the effect of diminishing the strength of the magnetic field above the inductor so that the electromagnetic forces limiting the cross-section of the head of the ingot are smaller. A more detailed description of the advantages of such a screen is presented in U.S. Pat. No. 3,605,865.
As do rectangular ingots cast by conventional continuous casting the ingots cast continuously with the above mentioned electromagnetic molds usually exhibit slightly concave sidewalls. The reasons for this disturbing effect are described in detail in the German patent publication No. DE-OS-28 48 808.
Electromagnetic molds for continuous casting are complicated and expensive, especially because of the small dimensional tolerances which have to be observed when making the molds. Also, a large number of ingot formats is normally required, which means that a corresponding number of molds has to be kept in store. It will be readily appreciated that this is economically unattractive.
Known from the German patent No. DE-AS 10 59 626 is a continuous casting mold with displaceable endwalls. The function and construction of a conventional continuous casting mold are, however, basically different from those of an electromagnetic mold; the special knowledge of one cannot therefore be transferred to the other. The conventional mold serves to conduct away the heat of the melt by direct contact with the melt. It also serves as the container for the melt and must therefore be sealed around its whole periphery.
The electromagnetic mold, however, does not come into contact with the melt. It serves to supply the electric current in a specific manner and contains facilities for influencing the magnetic field further.
For this reason special locking elements were developed for electromagnetic molds to permit variable positioning and fixing of the endwalls on the sidewalls--which makes it possible to vary the size of the mold opening and thus ingot cross-section. A special clamping device on the endwalls connects the relevant inductor parts to the screen so that there are always closed loops with the mold. This clamping device features a camshaft which, when rotated causes pistons to bring special contact elements into contact with each other. This clamping device, however, suffers the disadvantage that it has to be specially actuated for each of the contacts to be made between the end and sidewalls, and such that for uniform setting one requires exactly coordinated, synchronous movements. Furthermore the pressure applied to the contact elements depends solely on the rotation of the camshaft which, if made such that its motion is very easy, introduces the risk of the contact pressure being reduced while the mold is in service. Also the contact elements can be withdrawn from the clamping device only to the same extent as the height of the cam.
Accordingly, it is the principal object of the present invention to develop a clamping device for making the connection between the endwall and sidewalls, which does not exhibit the above noted disadvantages and, in particular, can be brought into use very quickly. Furthermore, the possible range for displacement of the compression piston and its pressure should be variable.